CA 19-9 (Carbohydrate Antigen 19-9)
The CA 19‑9 values measured are defined by the use of the monoclonal antibody 1116‑NS‑19‑9. The 1116‑NS‑19‑9‑reactive determinants on a glycolipid having a molecular weight of approximately 10000 daltons are measured. This mucin corresponds to a hapten of Lewis‑a blood group determinants and is a component of a number of mucous membrane cells.
3‑7 % of the population have the Lewis a‑negative/b‑negative blood group configuration and are unable to express the mucin with the reactive determinant CA 19‑9. This must be taken into account when interpreting the findings.
Mucin occurs in fetal gastric, intestinal and pancreatic epithelia. Low concentrations can also be found in adult tissue in the liver, lungs, and pancreas.
CA 19‑9 assay values can assist in the differential diagnosis and monitoring of patients with pancreatic carcinoma (sensitivity 70‑87 %). There is no correlation between tumor mass and the CA 19‑9 assay values. However, patients with CA 19‑9 serum levels above 10000 U/mL almost always have distal metastasis.
The determination of CA 19‑9 cannot be used for the early detection of pancreatic carcinoma. In hepatobiliary carcinoma the CA 19‑9 values provide a sensitivity of 50‑75 %. The concomitant determination of CA 72‑4 and CEA is recommended in cases of gastric carcinoma. In colorectal carcinoma, determination of CEA alone is adequate; only in rare CEA‑negative cases the determination of CA 19‑9 can be useful.
As the mucin is excreted exclusively via the liver, even slight cholestasis can lead to clearly elevated CA 19‑9 serum levels in some cases. Elevated CA 19‑9 values are also found with a number of benign and inflammatory diseases of the gastrointestinal tract and the liver, as well as in cystic fibrosis.
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